1. Field of the Invention
The present invention is related to a continuous mixer for mixing polymer materials such as plastics, rubber and the like.
2. Description of the Related Art
The above-described continuous mixer is normally designed so that strong shearing working is applied to materials to be mixed such as plastics, rubber and the like by rotors which rotate at a high speed in a counter rotation to plasticize, melt and mix them. A variety of fillers and additives are efficiently mixed into the plasticized and molten resins to mix and disperse them, thereby capable of making resin products of various qualities. Particularly, the continuous mixer of a center construction in which both axial ends of rotors are supported by bearings has the characteristics that the rotors are not deflected nor contacted with a chamber, thereby capable of rotating the rotors at high speed, and capable of easily constituting mixing and pelletizing equipment having the high production ability.
Out of such center support type continuous mixer, there is a two-shaft mixing apparatus having a twin-rotor and of a two-stage mixing type which is particularly suitable for tough mixing, which mixer comprises a pair of left and right rotors rotatably inserted, in the state of supporting axial both ends, into a chamber having a feed port and a compound discharge port on the axial both ends. The rotor for the two-stage mixing type continuous mixer as described above is formed with a first feed portion for carrying the mix from the feed port to the downstream, a first mixing portion for the compound materials carrying to the downstream by the first feed portion, a second feed portion for carrying the compound materials which was mixed by the first mixing portion, and a second mixing portion for further mixing the compound materials carrying to the downstream by the second feed portion, and in the halfway in the axial direction of the chamber, there is provided a gate device for controlling a mixing strength on the compound materials.
According to the two-stage mixing type continuous mixer, since a polymer flow resistance of the compound materials can be adjusted by the gate device provided in the halfway in the axial direction of the chamber, the mixing strength on the compound materials in the first and second mixing portions can be uniformed, thereby providing the advantage that the sufficient mixing time can be secured without excessively raising the temperature of the compound materials.
Further, according to the conventional two-stage mixing type continuous mixer as described above, volatile gases can be exhausted from a vent port provided immediate downstream of the gate device to thereby keep the better quality of the products, and the compound materials such as fillers can be added later from the vent port to thereby also accomplish the adjustment of the filling concentration thereof and the blend adjustment of the final products. However, in the conventional two-stage mixing type continuous mixer, from a viewpoint that the vent port mainly has a function as an exhaust port for volatile gases, the post-addition of the materials from the vent port is merely accomplished exclusively by a gravity drop of materials. However, problems which the post-addition of the materials can not be performed, takes place sometimes due to gases blowing back from the vent port.
That is, in the mixer of this kind, the compound materials as well as gases contained therein are introduced into the chamber from the first feed port, and the gases first introduced are blown back from the vent port to outside of the chamber, thus making it very difficult to evenly and sufficiently post-add separate compounds from the vent port. Further, the quantity of the gases first introduced into the chamber increases in proportion to a feed rate and a free volume of the continuous mixer, and therefore, particularly in the case of a large-type continuous mixer to meet the demand of recent high productivity, the blowing back of materials from the vent port is severe, and with respect to the filler having small bulk density, there is present a problem that the post-addition from the vent port is rarely performed.